Generally, technology of performing current position display, route guidance to the destination, and the like using road map data which is digital data representing information of roads in the real world have been known for navigation devices and the like. Such road map data often includes road network data of a plurality of levels according to the degree of detail, the scale display, and the like of stored road information, and has a structure in which the roads are represented by a connection relation of a plurality of links in the road network data of each level. Regarding a link ID for identifying each link forming such road network data, a structure has been known in which consecutive link ID numbers, according to the connection order within a link line formed of a plurality of consecutive links having a common attribute, are assigned to the links (for example, see Japanese Patent No. 3725022).
More specifically, in the road map data structure described in the Japanese Patent No. 3725022, the range of the link ID number is set for each link of the lowest level of the road network data of the plurality of levels. The plurality of links forming one link line are set with a range of the consecutive link ID numbers. For example, four consecutive links forming one link line are respectively set with link ID number ranges of 1000 to 1099, 1100 to 1199, 1200 to 1299, and 1300 to 1399 as the link ID. In the case where the plurality of links of a lower level are integrated to represent one link of a higher level, the link ID of each link can be represented by the link ID number range in the same manner as that of a lower level by integrating the consecutive link ID number ranges. For example, in this case where the four links are integrated as one link, the link ID of the link becomes 1000 to 1399.